Try a Hard Reset. You will have to catch it between boots, wait for the vibration...

[S]Power off the phone >[/S]hold Volume Down > [S]press Power >[/S] keep holding Volume Down until you seethe exclamation (!) screen, then immediately release the Volume Down

Now tap Volume Up / Volume Down / Power / VolumeDown

You should see the spinning gears and your phonewill reflash the last OS version held in recovery. You do lose data, but getyour phone back. Sign into your Microsoft Account and restore your backupduring the set up.

Alternately your Power button might be stuck. Also inspect that to see it has the proper "feel."

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What model device do you have. How old is it? Was it dropped or exposed to moisture? Do you have any ability to replace the battery and see if that fixes the problem? Batteries DO go and can be the issues although, I don't necessarily think that is the case here.

With all due respect - this is a notorious and recent fault. There are posts all over the internet about it, and Microsoft's response - playing dumb, not responding, and rolling our their "customer service" outsourced provider's staff in India to take the heat is, to say the least, underwhelming.

There is a notorious and serious problem with Windows Phones constantly re-starting. Hard resets do not resolve the problem.

It seems that the problem is rooted primarily in a buggy update that was recently rolled out - the one ending in "693". Apparently update "726" has a fix in it, but neither Microsoft nor its partner are giving any indication when this will be rolled out.

With all due respect - this is a notorious and recent fault. There are posts all over the internet about it, and Microsoft's response - playing dumb, not responding, and rolling our their "customer service" outsourced provider's staff in India to take the heat is, to say the least, underwhelming.

There is a notorious and serious problem with Windows Phones constantly re-starting. Hard resets do not resolve the problem.

It seems that the problem is rooted primarily in a buggy update that was recently rolled out - the one ending in "693". Apparently update "726" has a fix in it, but neither Microsoft nor its partner are giving any indication when this will be rolled out.

Any way to get a beta of the update? I know if the BlackBerry and Android world we can and do do this. :) Even in iOS it's possible to sign up and then download beta software. I'm pretty sure Microsoft has such a program. :)

Any way to get a beta of the update? I know if the BlackBerry and Android world we can and do do this. :) Even in iOS it's possible to sign up and then download beta software. I'm pretty sure Microsoft has such a program. :)

It is known as Insider Release Ring. They get the next push earlier than Production... Sometimes. Depends on a secret formula that the Insider team seems to know and I've yet to decipher.

Sitting at the airport.
Promised mother in law I would wait for her call.
My Lumia 650 is stuck on reboot mode.
Dang you Microsoft!
Its going to be a bad scene if and when I catch up to my much feared mother in law!?

Sitting at the airport.
Promised mother in law I would wait for her call.
My Lumia 650 is stuck on reboot mode.
Dang you Microsoft!
Its going to be a bad scene if and when I catch up to my much feared mother in law!?

Sounds like you fell victim to a bad OS build/update that was pushed recently. You'll likely need to connect the phone to a PC and use the Windows Device Recovery Tool. Or get a different device going forward. As a stopgap you could probably swap your SIM into a different phone.